Pulled two Inigos... both are minus atk... but I would still like to make the best use of him I can. One is + Res, the other is +Hp. Who do I sacrifice in the merge and what kind of build could i make for him to make him as good as I can possible make him?
How about you make him into a buffer/dancer unit? If anything, the addition of any dancer into a team makes for a good team. Especially Inigo, who buffs speed with his B skill. Give him a good C ability, and team buff sacred seal, or debuff sacred seal. I have played this game for around 2 months, and these are my thoughts about your predicament. I don't believe my advice to be the best, but it should help.
I don't see any problem with -ATK to be honest. Inigo's main goal is to deal with Reinhardt and Brave Lyn while giving your team some nice utility thanks to his Dance-skill. -DEF or -RES might be worse, but I could be wrong.
Whether you want to go with +RES or +HP is up to your own preference. +RES helps dealing with Reinhardts and other mages, while +HP gives him a bit more survivability against Lyn and Reinhardt.
I'd run the usual TA-Gronnraven-Bowbreaker set on him with a Distant Def-seal. C-Skill is up to you, and with this build you should be fine. :D
Imo Inigo is not a unit, that can be "destroyed" by unfavourable IVs like Brave weapon-users with -ATK-IVs.
(I know that the Gronnraven-tome alone is some heavy investment, but it's worth. He's my main dancer atm and I couldn't be happier.)
If you want a more budget-oriented build, you could simply run his default Dancer's Ring and give him Breath of Life-C-skill and seal.
B-skill could be Gale Dance, Escape Route or Wings of Mercy + an A-skill of your choice.
With this set he can function as a passive healer like Linde and her Aura-tome.
Passive healers are especially good in Chain Challenges or Tempest Trials, and with a dance-skill on top of the "regular" passive healer-set you'll have some nice utility. ^^
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